In the processing of fluids, such as water and waste water, it is necessary to separate materials from the fluid to render the fluid suitable for use or reuse. For example, as water purity standards increase, many stages of material separation may be required in order to output adequately clean water when the input water is dirty, such as in municipal waste water systems. In such municipal systems, after biological processes, further processes may include one or more flocculation stages designed to agglomerate very fine particles resulting from the biological processes. The very fine particles are less dense than the fluid, and may be referred to as finer, non-settleable-particles, as described below. The flocculation stages transform the very fine particles into particles that are denser than the fluid. However, significant amounts of such very fine particles may also be unchanged, or minimally changed, by the flocculation stage, and may not be denser than the fluid.
As a result of the density differences between the less dense fluid and the denser particles, in a settling process stage after a final flocculation stage, the denser particles move downwardly under the force of gravity as the fluid and the particles flow. In the settling stage, the denser particles are said to “settle” and form sludge (e.g., at the bottom of a basin), whereas the finer, non-settleable-particles do not settle. The fluid input to the settling stage may be referred to as “particle-laden fluid”, and may include the denser, settleable-particles and the finer, non-settleable-particles. The settled-particles at the bottom of a basin may be referred to as “sludge”. Sludge is characterized by a greater density of the settled-particles in a given volume than when the settleable-particles are flowing in the fluid. This settling may be referred to as “separation” of the settleable-particles from the fluid, whereas one aspect of “removal” (or “removing”) refers to taking the settleable, separated particles (sludge) from the material separation system. References herein to “fluid” are references to such “particle-laden fluid”, it being understood that “clean fluid” is the “particle-laden fluid” from which most of the settleable-particles have been removed (as by settling), and that “cleaner fluid” is the “particle-laden fluid” from which substantially all of the particles have been removed (as by settling, then filtering to an exemplary five micron level), and that “cleanest” fluid is the cleaner fluid after treatment such as ultraviolet radiation treatment.
As noted, because the significant amounts of the finer, non-settleable-particles may also be unchanged, or minimally changed, by the flocculation stage(s), the finer, non-settleable-particles are present in the fluid input to the settling process. Although the fluid output from the settling stage is substantially-free of the settleable-particles, that output fluid includes enough finer, non-settleable-particles that successive stages (e.g., filtration) are required for “separation” of the finer, non-settleable-particles from the fluid. Thus, following the settling stage, many filters must be provided to separate successively finer and finer, non-settleable-particles from the fluid. Lastly, additional treatment may be provided to the filtered fluid, as by ultraviolet treatment. Thereafter, in a clean water-collection stage, the cleanest fluid exits from the material separation system. As used herein, “removal” (or “removing”) also refers to taking the non-settleable separated particles from the filtering and/or treatment stage, if not also from the material separation system.
In the past, each of the particle separation and treatment stages has been provided with separate equipment for removing the respective particles from the particular stage, and each separate stage and removal equipment has been provided in a separate basin. In the settling stage many types of systems have been used, for example, to traverse the bottom of a settler basin and collect (e.g., via suction) the sludge. These systems operate only in the settler basin in which the settling process is being performed. Some types of suction sludge collection equipment have been configured especially for inclined-plate settlers in which the settled-particles are settling from between the plates onto the bottom of the settler basin, where the sludge gathers. Although improvements have been made to these systems, one design criteria has remained, namely, that the sludge removal equipment operates under the settler in the settler basin, separately from later basins that house later stages of the material separation and treatment system.
In the past, filtration stages have been provided downstream and separately from the settler basin. For example, in filtration basins separate from the settler basin, it has been typical to provide granular material on the floor of the filtration basins, and to configure the floor to be porous. The fluid and the finer, non-settleable-particles enter the filtration basin. The porous floors allow the fluid in the filtration basin to flow through the granular material, where the finer, non-settleable-particles are separated from the fluid. The resulting cleaner fluid exits the separate filtration basin without the finer, non-settleable-particles. However, these separate filtration stages have to be shut down to allow backwashing (i.e., removal) of the granular material. As an example of how removal has been provided, part of a filtration system has been by-passed during backwashing of that part, and a non-by-passed part has continued the filtration operations, but at a reduced rate of filtration. Alternatively, duplicate normal-rate filtration systems have been provided in parallel with each other, to allow one filtration system to perform filtering operations at the normal rate, while the backwashing is performed in the other shut-down filtration system. Thus each exemplary backwashing approach has a disadvantage that needs to be eliminated if more efficient separation and removal is to be provided.
A less-used way of continuously cleaning a filter for fluids in a flow stream uses different filter media. This filter media has been configured as a disk with a circular perimeter and some thickness. The disk has been mounted vertically on an horizontal axis and rotated. The fluid and the finer, non-settleable-particles flow perpendicularly to the rotating disk, and the fluid flows through the rotating filter media. The finer, non-settleable-particles are separated by the disk of filter media. A stationary suction unit has been placed next to the rotating disk on the side of the incoming fluid. The stationary suction unit removes filtered particles from the disk as the disk rotates past the stationary suction unit. Thus, the stationary suction unit does not have to move due to the rotation of the disk, and the filter unit is in a separate filter basin.
Another aspect of removal of particles from separation systems relates to improvements in settlers. One such improvement is the subject of the above-identified co-pending application. In the co-pending application, changes have been made in the configuration and orientation of settler plates, which are referred to as trays. The trays are mounted at a low-angle with respect to horizontal and are configured to define many narrow flow channels. A new configuration is that the settleable-particles settle from each flow channel, and rapidly settle into and are retained in a pocket defined by the tray configuration. Sludge forms in the pocket. The trays are provided in a vertically-spaced array, one tray above a next tray. From about fifty to about 250 vertically-spaced trays may be provided in one settler unit, for example. Another improvement of such low-angle tray settler is an ability to remove the sludge from each of the many pockets, and to do so without interfering with the settling operations that are ongoing between pairs of the trays.
These improvements contrast with problems that have arisen in attempts to make practical use of the theoretical design of a proposed clarifier apparatus in the form of a settler having at least two closely-spaced (e.g., one inch) flat thin-edge pates. The flat thin-edge plates have thin edges that allow a flow of particle-laden fluid into a narrow (e.g., 1 inch high) flow channel between the two closely-spaced flat thin-edge plates. As proposed, the flat thin-edge plates were horizontal, but as described below this proposed horizontal approach has to Applicant's knowledge never been successfully implemented even though the narrow flow channel enables a settling depth to be very short (e.g., slightly less than the narrow one inch height of the flow channel). As proposed, settleable-particles would settle through such settling depth onto a lower plate of the two flat thin-edge plates. Upon settling onto the lower flat thin-edge plate, the settleable-particles would form the sludge. Because the proposed flat thin-edge plate would be horizontal, there was a theoretical but unrealized benefit of somewhat shortening the length of the fluid-flow distance (e.g., horizontal) required to separate the settleable-particles from the particle-laden fluid to form the sludge on the lower flat thin-edge plate.
The problems that have arisen in attempts to make practical use of the theoretical design of these proposed closely-spaced horizontal flat thin-edge plates include the following. Even though the flow channel between two of these proposed flat thin-edge plates is very narrow (i.e., the one inch), it was intended that the settleable-particles would settle onto the flat thin-edge lower plate, and would form the denser sludge on the flat thin-edge horizontal lower plate. Thus, the result of the proposed two closely-spaced flat horizontal thin-edge plates was to confine the ongoing flow of the fluid through the narrow flow channel in the same space (or volume) that is occupied by the sludge. One problem identified by Applicant is that this proposed ongoing fluid flow would thus have a flow rate that would increase as the thickness of the settled sludge increases. The increase in the flow rate would be in a direction of the flow (e.g., an X direction), which is undesirable because it requires more flow length (X direction) to settle the settleable-particles from a fluid flowing at a high flow rate as compared to fluid flowing at a lower flow rate. This requirement is due to the higher flow rate fluid carrying the sludge in the narrow flow channel above the lower flat thin-edge plate, where such carrying would be in the X direction of the fluid flow. Applicant has observed that the higher flow rate would not allow the settling to occur rapidly in the downward (or Z) direction of the force of gravity (FG). Another problem observed by Applicant is that this carrying of the sludge in the X direction would offset (reduce) the goal of shortening the settling length (in the X direction), making it necessary to increase the length and thus the area of these types of proposed settlers. Additionally, it appears to Applicant that attempts to remove the sludge from between the closely-spaced flat horizontal thin-edge plates would interfere with the settling of the settleable-particles by mixing the previously-settled-particles with the cleaner fluid, which again would require more flow length in the X direction to do the same amount of settling and which reduces the practicality of this type of sludge removal impractical.
What is needed then is a way to more efficiently separate particles from particle-laden fluid. The more efficient separation should apply both to settleable-particles, and to the finer, non-settleable-particles. The more efficient separation should reduce inefficiencies of the many prior separate settling and filtration stages, and further provide more efficient sludge removal and finer, non-settleable-particle removal functions. An improved system should perform those more efficient removal functions using more efficient apparatus. Also, the needed way should provide practical methods and apparatus for removing the sludge from between closely-spaced trays of an improved settler, such as the settler of the co-pending application. There is a need for removal of sludge from a settler without having cross-flow of sludge and incoming dirty flow. Finally, there is also a need to allow each stage of filtration to continue full operations as the particle removal operation is performed, but to avoid the by-pass and duplication of equipment that characterizes prior filter systems.